The measurement of blood flow in superficial vessels of the body is usually performed with a continuous ultrasound Doppler system. For deep-lying vessels pulsed doppler must be used to resolve the range. However, pulsed Doppler systems are plagued by a range-velocity product maximum which makes it impossible for them to measure the fastest blood flows occurring deep in the heart. This invention describes a double repetition rate system which overcomes this handicap. Also described are several techniques for applying this principle to a practical clinical system.